Machine-switching telephone-exchange system



Aug. 7,v 1923.

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UNITED STATES heette? WARREN W. CARPENTER, OF BROOKLYN, NEW YORK, ASSIGNOB 'lO- WESTERN ELECTRIC COMPANY, INCORPORATED, OE NEW YORK, N. Y., A CORPORATION OF NEW Youn.

MACHINE-SWITCI-IING TELEPHOl'Il'E-EXCHANGE SYSTEM.

Application led December 31, 1919.

To @ZZ elf-hom t may concern: Y

Be it known that I, WARREN lV. CARPEN- TER, a citizen of the United States, residing at Brooklyn, in the county of Kings, State of New York, have invented certain new and useful improvements in MachineSwitching Telephone-Exchange Systems, of which the -following is a full, clear, concise, and enact description.

This invention relates to machine switching telephone exchange systems of the stepby-step type and more particularly to such systems involving' a number oi central oilices.

Conditions on commercial trunk and subscribers lines are such that a wide range of variation is encountered in the capacity, leak, length of line and voltage. This causes the impulse relay at each otiice, where the connection is built up .over a number of oiiices, to operate quickly and release slowly under certain of 'the above conditions, and to 'operate slowly and release quickly under other conditions. For example it the capacity, leak l'and voltage of a subscribers line or an inter-oiiice trunk, which is portion of the path "over which a connection is being built up and which includes one of the impulse relays, are all low, andthe trunk is long, 'the impulse relay will vbe slow to operate and quick to release; on the other hand, it the capacity, "leak and voltage are high and line lontrunk is short, the impulse relay will be quick to operate and slow to release.

It'will be readily seen tthat in .a connection being ybuilt iup over a number of intcrolice trunks with an impulse relay -in `the repeating circuitat eachoii'ice, the first relay directly in circuit with `the 'finger wheel or ysender and the second yimpulse relay in circuit lwith a back contact of the iirst. impulse relay and so on` that "due to the variables -m'entioned7 the impulse vrelays beyond the `irst in many cases would not transmit the "same number of impulses to the impulse relayor'relaysbeyond as was transmitted by the 'finger 'wheel to the iirstimpulse relay or theimpulses would be so distorted as notto be effective to perform. their Jfunction ot setting the Yswitches properly. ln some cases, the impulse relays farther along in the series would never get a chance to release; 'that is to say they `would hold up over the breaks caused byithe sender in the calling Serial No. 348,560.

volved and the setting up ot a wrong connection.

This invention provides a repeating arrangement which positively overcomes these diiiiculties and permits of the use of any number of serially connected interotlice trunks in the same connection with an impulse relay at each oi'lice and wherein any selective switch, no matter how far along 4in the chain of switches over which the call is progressing, being accurately set to the group determined by the particular digit of the wanted number with which such switch is involved, and wherein the adjustl ment ot the sender, relays and apparatus need not be as accurate as has heretofore. been required.

ln accordance with this invention, the circuit is so arranged that the set of impulses which is operating a given impulse relay in the series corresponds in number to that set transmitted to the first impulse relay at the originating oiiice, by the sender. How-- ever, the duration of each impulse transmittcd to the stepping magnet at a given oliicc is independent of the duration of the corresponding impulse in the trunk caused by the impulse relay at the preceding oiiice and is solely controlled by other factors which are readily controllable to eliect proper setting of the switches. The only requisite is that the impulse relay at a given office retract its armature momentarily a number ot times corresponding to the Ainterruptions caused by the sender in Athe original circuit, and since this is only dependent upon variables in the particular trunk in which it is included, this requirement can be easily met.

The period oi'l retraction of the armature of the impulse relay in circuit with the sender does not determine the period during which the impulse relay at the next oilice and those beyond are deenergized but each impulse relay upon its retraction starts a cycle ci operations oi a repeater at each oliice, the beginning and ending ot which deagain reaches its back contact due to the succeeding break in its circuit.

Referring tc the drawings, Fig. 1, shows the calling subscribers line, a line switch and a irst selector, the line switch brushes and multiples only, however, being shown.; Fig. 2 shows an interoliice trunk circuit including a repeater; Fig. 3 shows an incoming selector at the distant office; Fig. 4 shows a second selector; Fig. 5 shows a connector; Fig. 6 shows a private branch exchangelconnector; and Fig. 7 shows a trunk terminating before an operator which is one o11 a group accessible over a certa-in level of the first selector of Fig. 1.

Local calls.

Considering lirst a call between two subscribers in the same oice, it is only necessary in a call ot' this character to consider Figs. 1, 4 and 5 which should be placed in the order named from lett to right. Upon the extension by the line switch L S or". the calling line to an idle first selector. relay 101 thereof operates over the calling line circuit. Relay 101 operates show-release relay 102, over arms 113, (positionl.) ofthe iirst selector sequence switch or side switch which relay in turn operates relay 103. Relay 102 also applies ground to the third wire 144 leading back to the line switch to maintain the same operated in the welllnown manner. Relay 102 is locked up over a front contact of relay 103 to ground on the lower front contact of relay 101, this circuit being independent of sequence switch arms 112 so that upon the subsequent movement ol these arms, relay 102 and conscquently relay 103 will be iiiaintaiiied oncrated. Relay 102 in closing its upper contact completes a circuit over arm 110 including the sequence switch magnet 104 and its bach contact which magnet thereupon advances the sequence switch to position. 2, upon -its deenergization.

On the first interruption' of the line circuit by the sender at the calling station in transmitting the impulses representing the first digit of the wanted number, impulse `relay 101 releases causing stepping relay 105 to operate by its right winding over a circuit including the uppermost grounded armature and front contact of relay 103, back contact of relay 101, arm 112 (position 2) left armature and back contact oi relay 106 armature 181 and baclr contact or" relay 109 and back contacts of magnets of 111 and 107. Relay 105 at its inner left armature closes a circuit for energizing relay 106 over its lett winding and left nonsinductive winding of relay 105. The left-hand winding of relay 105 is merely a balancing resistance and has no magnetising effect upon the relay. Relay 106 in attracting its rleft armature locks to ground over arm 112 (position 2) the upper back Contact of relay 101, and the uppermost front contact of relay 103. Relay 105 locks up to the lower grounded front Contact of slow relay 102 over the armatures and baclr contacts of magnets 107, 111, its outer left armature and `iront contact, and arms. 113 (position 2). At its right armature, relay 105 operates the primary magnet 107 over arm 118 (position 2) causing the first selector to take one primary step, on the completion of which the magnet 107 by opening its baclr contact interrupts the locking circuit ot relay 105. Relay 105 releases, deenergizing the primary magnet. The loclring circuit for relay 106 is opened when the impulse relay 101 again attracts its armature as the sender closesy the line circuit at the calling station at the end of the first interruption provided relay 105 has released.

This completes the irst cycle of operations, l

and upon each subsequent interruption of the line circuit by the sender at the calling station the same operations ensue. Relay 108 which like relay 102 is oi: the slow release type operates in circuit with the primary magnet 107 and is maintained energized during the transmission of the impulses, con.

necting the grounded third wire 144 to the sequence switch magnet 104, this circuit not including the armature and back contact ot' the said magnet. When the impulses corresponding to the first digit of the wanted number have been transmitted, slow relay 108 releases, deenergizing magnet 104 which causes the sequence switch to advance to po sition 3. In position 3, relay is operated from ground on the lower front contact of relay 101, over arms 113. Relay 109 is operated over arm 100 (position 3) closing a locking circuit for relay 105, including the armatures and bac-lr contacts of magnets'107 and 111, the outer left armature and front contact of relay 105, and armature 171 and front contact ot relay 109. Relay 106 is en` ergized by its left winding from ground at the inner left armature and front contact of relay 105. Contacts 3 and 4 oit' arm 110 are strapped together and connected to ground. The sequence switchen arriving in position 3 therefore is moved into position 4 over a circuit including magnet 104 and its armature and back contact and arm 110. Upon arriving in position 4 the sequence switch magnet 104 is heldenergized in a circuit independent of its self-interrupting contact as follows: magnet 104, conductor 153, arms 113 (position 4) conductor 154, right front contact of relay 106, to the grounded third wire 144. In position 4, relay 109 is still energized over arm 100. In position 4, re-

step. The magnet, 111 at the end of its stroke opens the locking circuit ot relay 105 which thereupon releases.` The test brush 145 of the irst selector is now in engagement with test .multiple 146 ot the first trunk which we shall assume is busy and therefore grounded. Relay 106 in ,such event finds a locking circuit which holds it operated, after relay 105 has released, over the noninductive winding of relay 105 and its own lett front contact, arm 112, (position 4) conductor 145 to ground on the test multiple 146. Relay 105 is operated again whenv the armature of. primary magnet 111 reaches its back Contact, the circuit leading over the armatures and back contacts of the primary and secondary magnets 107 and 111, lowerinost armature and front contact of relay 109, lett armature and front contact of relay 106, arm `112 (position 4) tothe grounded test terminal 146. Relay 105 in attracting its outer left armature locks itself to ground over armature 171 of relay 109. Relay 105 in operating transmits another impulse to secondary magnet 111 to advance the selector to the next trunk. its locking circuit being opened when the magnet lllcompletes its stroke. Test brush 145 is now in engagement with the test multiple l146 ot the second trunk and assuming that this trunk is not busy it` will not be grounded and relay 106 will release when relay 105 retracts its inner lett `armature due to its circuit being opened by the secondary magnet 111. Relay 106' in retracting' its right armature connects the grounded third wire 144 to the test brush 145 and thence to the multiples 146 ot the seized trunk to render the same busy to other hunting iirst selee-tors. During the trunk hunting operation relay 106 at its right front Contact was maintaining sequence switch magnet 104 energized, this circuit leading` from the grounded third wire by way ot said rightv front contact, over conductor 144 and the arms 113 (position 4) conductor 153 to the sequence switch magnet 104, this circuit being independent of the armature and back contact of said magnet. On the release of relay 106 at the end of the trunk hunting operation the sequence switch magnet 104 deenergizes advancing the sequence switch to position 5. Upon the retraction of the right armature of relay 106 and consequent extension of the grounded third wire to the third wire 444 of the second selector, release relay 400 in the second selector circuit becomes energized'over arm 402. vRelay 400 in attracting its right armature closes a circuit for the sequence switch magnet 401 of the second selector, this circuit including arm 409 and the armature and back Contact of said sequence switch magnet, whereupon the second selector sequence switch is advanced by the magnet 401 to position 2. Relay 400 in position 2 locks itself over its left armature to .the second digit ot' the wanted number, the

irst interruption of the line circuit, causes impulserelay 101at the first selector to re` lease,operating stepping relay 105 thereat. The circuit is the same as previously de'- scribed since contacts 1 and 5 ot' sequence switch arms 112 are strapped together. Relay 105 in turn operates relay 106 which locks itself through its lett 'front conta-ct to ground through arm 112 (position 5) and back contact ot the line impulse relay 101. Relay 105, however, is now locked up over its outer left armature and front contact, arms 113,I (position 5) conductor 156 upper talking conductor,arms 403 of the second selector sequence switch (position 2) to ground at the armature and back contact of primary magnet 404 of the second selector. Relay 105 at its right armature closes a circuit through arm 118 (position 5) conductor 147, conductor 188, armature 155 and lfront contact of relay 103, lower talking conductor, arm 405 (position 2) ofthe second selector sequence switch through slow relay 406 to primary magnet 404. Magnet 404 is operated causing the second selector switch to take one step. Magnet 404 at the end ot its stroke unlocks relay 105 which in releasing releases magnet 404. When the line circuit is again closed by the senderat the end of the first interruption, relay 101 in attracting its upper armature unlocks relay l106 provided relay 105 has released. At the end of the series of impulses slow relay 406 releases. This relay is in circuit with the primary magnet 404 and has a similar Jfunction to slow relay `108 of the tirst selector. Relay 406 in releasing opens the circuit of sequence switch magnet 401 causing the second selector sequence switch to advance into position 3. Relay 407 is operated to ground over arms 403 (position 3) connecting this ground at its lett armature to the secondary magnet 408 of the second selector which rotates the test brush 413 into engagement with the test terminal 414 of the iirst trunk. rlhe sequence switch advances from position 3 to position 4 due to the permanent ground on the third contact of arm 409.` `Assuming that the `first trunk is busy a circuit is closed from groundon the busy test terminal 414 over arm 410 (positions 3 and 4) to hold up relay 400 over its ylett front contact after its alternative circuit is opened by arm 402 passing out of position 3. The same ground causes relay 407 to operate over arms 403 In position o,

quence switch magnet 401 over arm 409 which advances the sequence switch into po.- sition 5. Arm 410 in position 5 grounds the test multiple of the seized trunk to render the same busy.

release relay 400 is again operated from ground on the third wire 444 over arm 402. In position 6the upper and lower talking conductors of the irsty selector are connected over the arms 403 and 405 to the connector. In position 5 arm 410 of the second selector closes a circuit including release relay 500 of the connector, which in turn operates sequence switch magnet 501 over a circuit including its inner right armature conductor 521 and arm 502, advancing the connector sequence switch to position 2. The calling subscriber now operates his sender to send the third digit of the wanted number. Relays 101, 105 and 106 function inthe manner described. The impulse from the relay 105 of the first selector passes over the path traced including arm 118 position 5, conductor 188 armature 155 to the lower talking conductor tothe primary magnet 503 of the connector which moves the connector one step and releases relay 105 on the completion of its stroke. Slow relay 504 operates in this circuit and connects the grounded arm 505 (position 2) directly to the winding or' the sequence switch magnet 501. Succeeding impulses cause the connector to be stepped to the desired group. At the end of the series of impulses, slow relay 504 re,- leases, causing sequence switch magnet 501 to deenergize which advances the sequence switch into position 3. The calling party now operates his sender to transmit the last digit of the wanted number. Secondary magnet `506 is then operated in the same manner as described for magnet 503, magnet 506 being substituted for magnet 503 in the stepping circuit by arm 510. Upon the cessation ot the impulses, slow relay 504 releases, advancing the sequenceswitch to position 4. Vhen the arm 502 moves oiip its third and onto its fourth contact a circuit is closed including the sequence switch magnet 501 and its armature and back contact. Contacts 4 to 13 are strapped together and v connected to ground. Consequently the se zquence switch is advanced to position 14. VVhilethe sequence switch is advancing to position 14 the selectedlline is being tested. If the line is busy, relay 500 is held up over its inner left armature in positions 5 and 6 of arm 507 to ground on the test terminal 514 of the busy line. The connection of the `grounded third wire 544 to this relay is opened as arm 520 leaves position 4. "When the sequence switch reaches position 14, busy tone is connected by arm 509 to the upper talking conductor. While the connector sequence switch is advancing from positions v6 to 13, ground is connected over the inner right armature and 'front contact of relay 500, conductor 521, arm 509, upper talking conductor to the irst selector. GrroundV is also connected through the arm 510, lower talking conductor to the irst selector causing magnet 104 of the lirst selector sequence switch to advance the sequence switch to p0 sition 6. This circuit leads from the lower talking conductor (Fig. 1) front contact and armature 155 of relay 103, conducto-rs 188,

tact of relay 105, arm 110 (position 5) to magnet 104. In position 6 this magnet is held up to the grounded lower talking conductor in a circuit including magnet 104, conductors 153, 190 and arms 113. The ground over arm 509 of the connector sequence switch to the upper talking conductor operates ringing cutoli' relay 133 at the iirst selector, this circuit leading from the upper talking conductor (Fig. 1) over conductor 156 at the first selector armature 181 and front contact of relay 109, left back contact of relay 106, arm 112 (position 6) right winding of relay 133 to battery. Relay 133 in attracting its inner right armature locks itself to the grounded third wire 144 over a back contact 192 of relay 148.

Vhen the connector sequence switch arm- 510 moves out of its thirteenth position, the circuit traced for the magnet 104 of the sequence switch of the first selector over the lower talking conductor is opened, whereupon the first selector sequence switch advances to position 7. This is the ringing position, but since ringing cut off relay 133 is now operated, ringing cannot take place. ln position 7, ground from the right outer front contact of relay 133, arms 118 and 110 causes sequence switch 104 to advance the sequence switch magnet to position 8. ln position 8 the talking circuits are connected from the calling subscriber to the connector due to the energization of relay 148, the circuit 'for this relay including the uppermost armature and front contact of relay 103, arm 100 (position 8), arm 118, retracted right armature of relay 105, arm 110 (position 8) kto battery through the sequence switchmagnet 104. Magnet 104 ismarginal and does not operate in this circuit. The operation of the relay 148 extends the busy tone circuit including the upper talking conductor over its upper :front contact to the calling subscribers receiver through condenser 150, and a normal contact of relay 186 the return being over the lower talking conductor to batterythrough the lower winding of relay 101.

Vhen the calling subscriber hangs up his receiver, relay 101 releases causing relays 102 and 103 to release in turn. The release of the uppermost armature of relay 103, removes ground from relay 148 which in retracting its armatures opens the connections 147, arm 118 (position 5), normal right con` to the talking brushes of the irirst selector to prevent possible interference with `established connections as the brushes wipe over the multiples. kGround from the lower back contact ot relay 103 Icauses the release magnet 135 o1 the lirst selector to operate to restore the first selector to normal position. Upon reaching its normal position, oit-normal contact springs 136 connect ground from the lowerinost back contact o1 relay 103 over arm 110 (position 8) to sequence switch magnet 10-1- which advances the sequence switch to position 1. `lVhen the relay 101 releases and deenergizes relay 102, this relayby the retraction ot its lower armature removes ground from third wire 144 which restores the line switch and also releases relay 400 of the second selector. Relay 400 in retracting its right armature closes a circuit including the contact springs 411, which are operated only on the4 eleventh rotary step of the selector over arm 409 (position 6) for sequence magnet 401. The second selector sequence switch thereupon moves 'from position 6 to position 15 over this circuit. i llVhen arm 409 rcachesits iftecnth position it inds ground directly at the right armatureand back contact of relay 400, whereupon the second selector sequence switch continues to advance to position In position ground on arms 403 operates release magnet 412 or the second selector, which restores thevsecond selector to normal. Upon reaching its normal position this selector restores off-normal springs 413 whichy close a` circuit including arm 409 to sequence switchmagnet 401, advancing the sequence switch to 'position 1. When the second selector sequence switch arm 410 moved out ot position 6 it removed ground from thethirdwire 544er the connector switch causing relay500 thereat to release. Ground from thepinner right back contact of relay 500 and arm 502 (position 14) of sequence switch magnet causes the connector sequence switch to advance to position 16. Relay 500 is operated in position 16 'from ground on arm 505. i TheA inner right front contact oit relay 500 connects ground to the sequence switch. magnet 501 over arin 502 (position 16) causing the sequence switch to advance into position 17. Relay 500 releases as arm 505 moves outot position 16 and its inner right back contact connects ground tothe seventeenth to twentyfirst contacts ot arm 502, advancing sequence switch into position 22. Release magnet 512 is operated inposition 22 over off normal springs 513 from ground on arm 505 causing the connector to return to normal. Upon restoration, the connector closes oft-normal springs 513 which close a circuit jfor `magnet 501 over arm 502 to advance sequence switch to normal. y l

Assuming now that the selected line had been idle. An idle condition is represented quence switch to advance to position 6 as on a busy connection. Due to the line being idle and consequently rela-y 500 being inert, no ground is present on the upper talking conductor at this time and consequently the relay 133 is not operated as it was in the case of a busy line.y When the connector sequence switch advances int-o position 14 the tirst selector advances to position 7 as described in the case of a busy line. Due to rela-y 500 being inert the sequence vswitch moves out or' positions 14 and 15 into position 16 over arm 502.y In position 16 relay 500 energizes over arm 505, advancing the sequence switch out of position `16 and into position 17. 1n this position the talking conductors are connected through to the calledk line. The iirst selector sequence switch` in position 7 connects ringing generator and ground to the called subscriberss line over the upper and lower conductors respectively. This circuit includes the. left winding of relay 133, arms 113 (position 7) armature 155 and front contact of relay 103, lower talking conductor, the bell at the called station and returning over the upper talking conductor, conductors 156 and 160, front contact and armature 13,1 ot relay` 109, lett armature and back contact or relay 106 to ground over 112 (position 7). l/Vhen the called subscriber answers, the removal of his receiver closes an operating circuit for the ringing cut orf relay` 133, which locks itself over its right winding and its inner right armature and tront contact, Contact 192 of relay 148, to the grounded third` wire 144. Relay 133 in attracting its outer right armature closes a circuit to operate sequence switch magnet 104 which advances the lirst selector sequence switch to position 8, this circuit including arms 118 and 110. rlransmission circuits are closed in posit-ion 8 by theoperation of relay 148, this relay `as in the case of the busy call operating over the following circuit: uppermost armature and front contact of relay 10,3, arm 100 (position 3), relay 148, arm 11S (position 8), right armature and back contact or relay 105, arm 110 (position 8), to battery through the sequence switch magnet 104 which, as hereinbefore stated is marginaly and does not operate in this circuit. Since the connector sequence switch is now in position17, the operation of relay 14S closes a circuit for feeding talking current to the called line.

i relay 106 to ground.

over relay 106 at the first selector. This circuit includes the lett winding of relay 106, arms 113 (position 8) of the first selector sequence switch and armature 155 and front contact of relay 103, lower talking conduct-or, the called line, upper talking conductor, conductor 157, armature 191 and front contact of relay 148, right winding of Talking current is fed to the calling line over the windings of relay 101. The calling and called ends o1 the connecting circuit are inductively united but conclue-tively separated by a pair of condensers 150 and 151 in accordance with wellknown practice.

In the case of a successful connection, the release of the first and second selectors takes place as described in connection with a busy line, but the release of the connector is slightly diiierent, since it is now in position 17 instead of position 14. Then ground is removed'from the third wire 544 upon the release oi' the second selector', relay 500 in releasing connects ground at its inner right armature to arm 502 (position 17) causing the sequence switch magnet to advance the sequence switch to position 22. in position 22 the circuit for the release magnet 512 is closed which in ,operating restores the connector, and the oit-normal springs 513 restore when the connector reaches its normal position and advance the sequence switch to position 1, as described in the case of abusy line.

I meroce calls. y

Considering now the case of a call `e.\: tending through a plurality of oiiices. .ln tracing such a call Figs. 1, 2, 3, 4 and 5 are to be placed in the order named. When the first selector, (Fig. 1) is set opposite a level containing the outgoing trunk group desired and has seized an idle trunk therein, the relay 106 Fig. 1, in releasing as bef-ore described extends the grounded third wire 144 to conductor 244, resulting in the operation of relay 201 of the repeater. Relay 106 also in releasing advances the i'irst selector sequence switch to position 5, as described in the case of a local call. Relay 201 in operating closes a circuit from ground, relay 202, uppermost 'contact of relay 201, upper talking conductor to the interoiiice incoming selector at the distant oiiice, impulse relay 300 thereat returning over the lower talking conductor, back contact of relay 207, lowermost front contact of relay 201 to battery through relay 203 causing relays 202, 203 and 300 to operate. Relay 301 does not operate in this circuit since it is short-circuited over a back contact of relay 318. Relay 300 operates slow7 relay 302 over the arms 308 (position 1) or the incoming selector sequence switch. Relay 302 in turn operates relay 303. Relay 303 at its armature 325 connects the lower grounded armature of relay 300 to the slow relay 302 independently of the arms 308. These circuits are similar to those of the first selector. Relay 302 connects ground at its upper armature through arm 304, (position 1) to the sequence switch magnet 305, causing the sequence switch to advance into position 2. When the calling subscriber operates his sender for the second digit of the wanted number, the first retraction of the larmature of relay 101 operates relay 105 as before described, which in attracting its armature locks itself over the following circuit: right winding of relay 105, back contacts of the primary and secondary magnets 107 and 111, outer left armature and front contact of relay 105, arms 113, (position 5) upper talking conductor armature 208 and front contact of relay 201 to ground at the front contact of relay 202. A circuit is also closed by relay 105 to operate relay 205 as follows: right armature and front contact of relay 105, arm 118, (position 5) to the lower talking conductor over the conductors 147, 188 and armature 155y and front contact of relay 103, armature 209 and front Contact of relay 201, relay 205, to free pole of battery. The operation of relay 205 opens the trunk loop to the distant ofiice causing relay 202 of the repeater and the impulse relay 300 at the distant oiiice to release and connecting ground to hold relay 203 operated for a purpose to be described. The release of relay 202 unlocks relay 105. Relay 105 in retracting its right armature causes relay 205 to release which again closes the trunk loop to the distant office causing relays 202 and 300 to again energize. On the retraction of the upper armature ot the impulse relay 300, at the incoming selector when the loop circuit was opened by relay 205 of the repeater, stepping relay 306 operated over a circuit including the uppermost armature and front contact of relay' 303, the upper back contact ot' relay 300, arm 315, (position 2) left back contact of relay 307, outer right back contact of relay 318, inner left armature and back contact of relay 311, armatures and baclcontacts of secondary and primary magnets 310, 313, winding of relay 306 to battery.

Relay 306 in attracting its outer left armature locks itself over arms 308, (position 2) to the lowermost front contact of relay 303. In attracting its inner left armature, relay 306 operates relay 307 in a circuit including the noninducting winding of relay 306. Relay 307 locks itself to ground at the retracted upper armature of impulse relay 300 over the following circuit: left winding of relay 307, left winding of relay 306, conductor 352, outer left armature and left back contact or relay 318, left armature and Jfront contact of relay 307 arm 315 (position 2). Relay 306 in attracting its right armature, connects ground over arm 314, to the primary magnet 310 causing the incoming selector to be moved one step. At the end of its stroke, magnet 310 opens the locking circuit of relay 306 as in the iirst selector selecting operations. Re lay 306 opens the original circuit for relay 307, and this relay releases ir" relay 300 has pulled up. On completion ot' the series of impulses, slow relay 309 which was operated in series with magnet 310 during the transmission of the impulses, releases, opening a circuit through sequence switch magnet which was closed upon the initial operation of relay 309, the circuit including conductor 344 and the lowermost armature and 'front contact ot relay 303. The sequence switch advances to position 3, in which position relay 306 is operated over the arms 308, to ground at the lower lront contact ot relay 300. Relay 306 operates relay 307 in this position. Relay 311 operates t'romground supplied over arm 312 position 3 and the uppermost front contact ot relay 303. Sequence switch magnet 305 operates from ground on arm 304, position 3, causing the sequence switch to advance to position 4. Sequence switch magnet 305 is held energized in position 4 from ground through the arms 308, through the right front contact ot relay 307 to the grounded third wire 344. Relay 306 is held up in position 4 over its outer left Contact and inner right armature of relay 311. Relay 306on position 4 operates secondary magnet 313 over outer right armature ot rela-y 311, through arm 314 (position 4) to ground at the right front contact ot relay 306 causing the selector switch to take one step connecting the test brush 320 to the test multiple 321 of the iirst selector in the group. Ii' this trunk is busy relay 307 will be held energized, after stepping relay 306 releases, as its circuit is opened b vniagnet 313, over a circuit including the noninductive winding of relay 306, outer left armature of relay 318, conductor 353, left armature and front contact of relay 307, arm 315 (position 4) to the grounded terminal 321. `Relay 306 operates when magnet 313 closes its back contact from the same ground on the busy terminal 321 and imparts an impulse to the magnet 313 to step the selector to the next trunk which is assumed to be idle. The cir cuit for relay 306 is as follows battery, right winding of relay 306, armatures and back contacts of magnets 313, 310, outer lett armature and front contact of relay 311, conductor 326, outer lett armature and back Contact of relay 318, conductor 353,.le'ft armature and front contact et relay 307, arm 31.5(position 4) to ground on the busy multiple321. As-

c suining tliesecondvtrunlr to be idle relay 307 l thereuponk releases, l movement and at its right armature extendf ing the grounded conductor 344to conductor preventing stepping 320 and to the seized trunk test terminal to render the same busy. The retraction of the right armature of relay 307 opens a circuit to the sequence switch magnet 305 which advances the sequence switch to position 5, as in the case of the first selector. The operations of setting the second selector and connector need not be described since they are similar to those described for a local call, the impulses beingtransmitted from the impulse relay 300 oi. the incoming selector, instead of from impulse relay 101 of the first selector.

Assuming therefore that the calling sub-- scriber has transmitted the hundreds. tens and units impulses and that the line selected is busy, as liereinbefore described, the

sequence switch of the connector advances i .trom position 6 to 13 upon the termination of the units impulses, and the relay 500 is locked up, and at its inner right armature grounds the upper talking conductor through these positions, arm 510 simultaneously grounding the lower talking conductor. The ground applied'to the lower talking conductor over arm 510 closes a circuit leading back to the incoming selector oassinef toconductor 343 through contact 328 oit'l rela i 303 conducto-r 330 arm 314 I d a i 7 (position o) right armature and back contact of relay 306, arm 304, (position sequence switch magnet 305 to' batterycausing the interoliice incoming selector sequence switch to advance Vinto position 6. ln position 6, arms 308 of the incoming selector sequence switch again close a circuitl toy energize the sequence switch magnetA 305, this circuit however being independent ot the armature and back contact et' saidmagnet. This circuit is the same as that traced includingI tlic lower talking conductor, but

instead ot passing by conductor 330 and over arm 314, it passes directly to; arms 308 (position 6) and directly ktothe magnet 305. In position 6 rela-y 318 is operated over'alrm 312 to ground at the uppermost armature and front contact of relay 303. Relay v318 in operating, locks itself to the grounded third wire 344 over its inner right armature.` Re'- lay 318 in attracting its outer right armature extends conductor 324 connected to the grounded upper talking conductor to the right winding of the ringing cut-ott relay 317, over the left back contact of rela-y 307 and arm 315 (position 6). The ringing cutoit' relay 317 thereupon operates and at its inner right arma-ture and front Contact locks itselito the grounded third wire 344 over armature346 and back contact of rela-y 319. When ground at the connector is removed Vfrom the lower talking conductor, as deies scribed, sequence switch magnet 305 releases and advancesthe sequence switch to position 7. Relay 317 being operated, at its outer right armature now closesv a circuit ,over `314 (position and the,` right removed leoarmature and bac-k contact of relay 306, arm 304, magnet 305 to advance the sequence switch to position 8. ln position 8, relay 319 is operated vover arm 312 and the uppermost armature and front contact of relay 303. r1`his relay attracting its outer armatures stende the upper and lower talking conductors oi' the second selec-tor through to the corresponding conductors of the incoming selector. When the relay 318 operated as the incoming selector sequence vswitch moved to position 6, it opened at its inner left armature and back contact ashunt about the high resistance relay 301 resulting inv the deenergiaation of a marginal relay 203 in the loop circuit leading back to the repeater and including relays 203, 300 and 202. Y The introduction of this high resistance in series in the trunk loop leading back to the originating oiiice causes relays 202 and 203 thereat, as well as a relay 300 in the incoming selector circuit to release. llelay 301 in operating applies ground to conductor 3-10 leading to slow relay 302 to maintain relay 302, and consequently relay 303 energized after the circuit ot relay 302 is opened atthe lower armature and back Contact oi relay 300 to prevent premature release. lVhen relay 203 in the repeater released, it connected ground through the lett iront contact of slow relay 204C to relay 206 which thereupon operator. and locked itself tothe grounded third wire 244k. Relay 206 in attracting its armatures applies ground to the upper and lower talking conductors lead g back to the first selector which causes the lirst selector to function in the same nia-nner as it did in the case of a local bus-y line, that is to say, ground supplied iiroin the lower back Contact ol relay 203, leflt iront Contact of relay 204, armature 210 and iront Contact of relay 206, lower talking conductor to `the irst selector circuit, front contact otrelay 103, conductors 188, 1417, arm 118, (position right back contact oi relay 105, arm 110, sequence switch magnet 10d to battery. Magnet 10a advances, the sequence switch of the iirst selector to position 6 in which position arms 113 connect magnet 10e; directly to the lower talking conductor over the front contact 155 of relay 103. The magnet 1011 holds up in this circuit, since this circuit does not include its seit-interrupting contact. lVhen the ground is removed from the lower talking conductor, magnet 104; dee-nergizes ,advancing the sequence switch to position 7. This ground is from the lower talking conductor when the relay ture. Relay 207 is deenergized due to the retraction ot the right armature of slow relay 204; which in turn is deenergized due to the opening of its circuit at the front contact of marginal relay 203. Due to ground being present on the upper talking con- 204 retracts its left armaductor from lower armature and front contact of relay 207, and lower armature and front contact of relay 206, simultaneously with the ground on the lower talking conductor, this ground remaining until after the first selector sequence switclr arrives in position 6, ringing cutoil relay 133 is operated in a circuit leading over the upper talking conductor, conductors 156, 160, armature 181 and front contact of relay 109, lett armature and back contact or relay 106, arm 112, (position 6) right winding of ringing cuto'll relay 133 to battery. This relay in attracting its inner right armature locks itself to the grounded third wire 144 and in attracting its outer right armature advances the sequence switch to position 8 as in the case vof a local busy call. The circuitfor advancing the sequence switch to position 8, leads over the outer right armature of relay 133, arm 118 (position 7) right armature and back contact oi relay 105, arm 110, self-interrupting contact of magnet 10-1, winding of said magnet to battery. In position 8, relay 1118 is operated over the Jfollowing circuit: uppermost armature and front Contact oft relay 103, arm 100v (position 8) relay 14:8, arm 118 (position 8) right armature and back contact of relay 105, arm 110, magnet 10a to battery. Magnet 1041 does not operate in this circuit but the relay 148 operates and connects the upper and lower talking conductors of the first selector to those of the trunk repeater circuit. W'hen the relay 206 in the repeater operated, this relay in addition to grounding the upper and lower talking conductors with the results described, also at'its uppermost armature opened the circuit of relay 201. This relay in retracting its armatures disconnects the repeating apparatus from the talking conductors and extends the talking conductors from the Erst selector directly through to the talking conductors of the incoming selector at the distant oiiice. When the iirst selector sequence switch arrives in position 8, the Jfollowing circ-uit is closed for the called vsupervisory relay 106, free pole of battery, lett winding of said relay, conductor 170, arms 113, (position 8) conductor 188, front contact 155 of relay 103, lower talking conductor to the incoming selector ot' the distant oiiice, high resistance relay 301, and bridged relay 300y thereat returning over the upper talking conductor, conductor 157 Jfront contact of relay 1118, right winding or' relay 106 to ground. y

Referring now to the connector circuit, it will be recalled that upon the setting o1' the connector on the line, the sequence switch of the connector advances from the third to the fourteenth position. 11 the line is busy, the relay 500 is locked up as has been described and consequently the sequence switch magnet circuit is opened at the inner right armature and back contact of the relay 500. ln position 14, busy tone current is transmitted over sequence switch arm 500 to the upper talkingr conductor and thence to the calling' line through the condenser 335 in the incoming' `.selector circuit and condenser 150 in the lirst tor circuit, returning' over the lower talking' conductor through the lower winding ot the 1elay 101 in the lirst selector' circuit.

The calling subscriber upon hearing the busy tone replaces his receiver causing the release ot relay 101 and consequently relays 102 and 103 in the first selector circuit whereupon the i'irst selector and the tirst selector sequence switch are restored as described in the ease ot a local call. The removal of ground from the third conductor 144 upon retraction o t the lower armature ot relay 102 releases the relay 206 ot the repeater, thus restoring the repeater apparatus to its normal condition. The release ot the armature 155 ot the relay 103 opens the loopy circuit extending to the distant oitice whereupon the relay 301 retracts its armature removing ground -trom conductor 340 thusrelfzasing` relays 302 and 303. Relay 303 in retraeting its lowermost armature closes the 'followingl circuittor the release magnet 341 ot the incoming selector; tree pole ot battery, magnet 341, ott-normal contact 342` to the lowermost back contact otl relay 303. The retraction ot the lowermost armature of relay 303 in removingground from the third wire 344 and consequently trom the third wire 444 ot the second selector causes this switch and its associated sequence switch to release in the manner described in the case of a local connection. Arm'410 of the second selector sequence switch in restoring removes ground from the third wire 544 leading to the connector which likewise causes the restoration of this switch and. the associated sequence switch as described in the case ot a local connection,

Assuming, however, that the selected line had been idle, in this event therelay 500 in the connector is not locked up while the` sequence switch is passing .trom position 3 to 14 and consequently no ground is applied to the upper talking` conductor since the inner right armature ot relay 500 is resting on its back contact. Consequently when the arm 510 passes ottl its thirteenth contact and removes ground from the lower talking conductor which ground has been holding up magnet 305 in position 6 ot the incoming selector circuit, the incoming selector sequence switch does not pass directly out of position 7 since the right armature of the ring-ing cutoff relay 317 is retracted owing' to the tact that the right winding ot thisrelay did not iind a circuit leading over the upper talking conductor. In position 7 ot the incoming selector sequence switch, ringing current is 'applied to 'the selected line over the following circuit: ringing generator, lett winding ot relay v317, arm 303 (position 7) armature 323 ot relay 303, conductor 343 to the lowery talking,- conductor ot the second. selector, arm 405, (position 6) arm 510, (posit-ion 17) through the hell oit the selected station returning' over the upper talkingl conductor, arm 509, position 17) arms 403, (position 6) conductor 324, outer right armature and front contact ot relay 318, lett back contact of relay 307 to ground over the arm 315, (position 7). Relay 313 is energized in positions 6 and 7, over arm 312 to the uppermost front contact ot relay 303. This relay will have operated in position 6, `openingV the shunt about the high resistance relay 301 which resulted in the deenergization ot the marginal relay 203 at the originatiup,- otlice and the release ot this relay will have caused the advance ot the iirst selector sequence switch to position 8 as described in the case ot a busy con-iv nection. Ringing` tone is transmitted to the calling line by induction through the windings ot relay 317, lli/Then the called subscriber removes his receiver, the ringing` cutott relay 317 operates cutting ott the ringing current and locking itself over its inner right armature and a back contact of relay 319 to the grounded third wire. This relay in attracting` its outer right armature ad-' Vances the sequence switch to position 3 over arm 314, (position 7), right armature and back Contact ot relay 300, arm 304, armature and hack contact ot the sequence switch i magnet 305 to battery; rlhe magnet 305 thereupon advances the sequence switch to position 8. in this position relay 319 is operated over arm 312 to the uppermost front contact ot' relay The energization ot relay 319 extends the talking conductors oitthe incoming' selector to the talking` conductors ot the second selector and causes the operation ot relay 307 over the following' circuit: tree pole battery, lett winding ot relay 307, conductor 350. arms 303, (position 3) armature 323 and front contact ot relay 303 to the lower talking conductor and thence to the called line, returning overthe uwer talking conductor. conductor 345 'contact ot relay 307, arm 315, (position 3) conductor 343 to the lower tallvringconductoi'" 347. The resultant increase in the current causes the relay 10G of the tirst selector of the distant oiiice to energize which may be used for supervision or for operating4 a meter. When this high resistance relay is short-circuited relay 300 immediately operates closing a substitute ground to hold up relayl 302 and consequently relay 303 after the. relay 301 has released. lThe parties may now converse, talking current for the calling subscribers station being fed over the windings of relay 101, at the originating office and talking current for the called subscribers station being fed over the windings of relay 307 at the distant otlice. The release of the connection upon the restoration of the receiver of the calling party to its switchhook takes place as described in the case of a busy line.

Private branch exc/16mg@ connections.

Considering now the operation of the system in selecting one of a number of lines leading to the same station as for example a private branch exch-ange.

Referring now to Figs. 1, 4 and 6 and assuming that the second selector of Fig. 4

has seized a private branch exchange connector shown in Fig. 6, the operations from this point will now be traced. It will be recalled that in the operation of the second selector when` this switch seizes an idle trunk, arm 410 in position applies ground to the test multiple 414 or" the seized connector. Similarly, in Fig. 6, when the secl tion 1) ond selector of Fig. 4 seizes an idle P. B. X. connector, Fig. 6, arm 410 in position 5 applies ground to test multiples 600 of the seized connector, and consequently to test Wire 644, this ground being extended over arm 601, conductor 620 to release relay 602 which relay is similar to relay 500 in the connector. In attracting its' inner right armature this relay advances the sequence switch to position 2 over arm 603 (in posi- Relay 602 locks itseli:` to the grounded third wire 644 over its inner lett armature and front contact. Upon the operation of the sender by the calling party in transmitting the tens digit of the wanted number, the primary magnet 604 is operated over `the lower talking conductor and arm 605 to step the connector in a primary direction to the desired group. vThe slow relay 606 at the termination of the impulses releases, opening the circuit olf the sequence switch magnet 607 which thereupon advances the sequence switch into position 3. Iniposition 3 upon the operation of the sender by the calling party, impulses are transmitted to the secondary stepping magnet 608, in accordance with the units digit of the wanted number, which magnet steps the switch and into engagement with the rsttrunk of thel group leading to the desired private branch exchange. Upon the termination ot this series of impulses, the slow relay 606 releases deenergizing sequence switch magnet 607 which advances the sequence switch to position 4. Arm 601 in leaving position 3 opened the locking circuit of relay 602. Relay 602 in releasing its inner right armature advances the sequence switch magnet 607 over arm 603 advancing the sequence switch to position 5.

Assuming that the first trunk is busy oi grounded, a circuit is closed to operate relay 610 over the arms 611, (positions 4 and 5),

conductor 622 to grounded multiples 609, 616. Relay 610 closes the following circuit for relay 602: :tree pole of battery, relay 602, conductors 620, 619, outer left armature and front contact of relay 610,4 armatures and back contacts of magnets 608, 604, conductor 618, inner left armature and front contact of relay 610, conductors 617, 612, 613, arm 615, (position 5)'and grounded multiple 616. Relay 602 in attracting its outer right armature closes the following circuit for magnet 608 to advance the connector to the neXt trunk: grounded outer right armature of relay 602, conductor 621, inner right armature'and front contact of relay 610, conductors 624, 625, magnet 608, slow relay 606 to battery. Magnet 608 at the end of its stroke opens the circuit of relay 602 which releases its outer right armature deenergizing magnet 608. 1f the multiple 609 in this trunk is not grounded, relay 610 releases and the multiple 616 not being grounded, and relay 610 being inert, relay 602 cannot energize when the break in its circuit at the back contact of magnet 608 is closed. Relay 606 was energized during these impulses and upon releasing deenergizes the sequence switch magnet 607 whereupon the sequence switch is advanced to position 6, in which position vand subsequent positions arm 615 grounds the test multiples to render the seized trunk busy.

In posit-ion 6, relay 602 is energized over conductors 620, 628, arms 611 to ground. Relay 602 at its inner right armature and arm 603, (position 6) advances the sequence switch to position 7. Contacts 7 to 16 being grounded sequence switch moves immediately into position 17 and relay 602 being at this time inert connects ground at its inner right armature and back contact and arm 603 to the sequence switch magnet 607 which advances the sequence switch to position "19.* In position 19, the relay 602 operates over the following circuit: free pole ot battery, relay 602, conductors 620, 628, arms 611, position 19 to ground. Relay 602 in attracting its inner right armature advances the sequence switch over arm 603, into position 20, which is the talking position. Arm 605 in passing from positions 9 to 16 grounds the lower talking conductor leading back to the irst selector just as in the case of a call to an ordinary subscriber as hereinbefore described with the same results. Talk ing current is fed to the calling and called lines from the first selector as in the case of a connection to an ordinary local line.

Then the calling party breaks down the connection, ground is removed from the third wire 644 which causes the release of relay 602 which upon being operated in position 19 locked up to the grounded third wire 644 over its inner lett armature and arm 601. This relay in releasing its inner right armature closes a circuit including arm (position 20) and the sequence switch magnet advancing the sequence to position 22. ln this position, the release magnet 629 is operated over the following circuit: tree pole of battery, magnet 629, oli normal springs 630, arms 611 (position 22) to ground. Then the switch reaches its normal position and restores the olf normal spring 630, a circuit is closed for the sequence switch magnet 607 as follows: magnet 607, its armature and back contact, arm 603, (position 22) conductor 631 to ground at the ol3 normal springs whereupon the sequence switch advances to normal position. p

Assuming now that all the private branch exchange trunks are busy, the connector will step over these trunks to the last trunk where it will stop, and result in a busy signal being given to the calling party. Terminals 609 and 616 of the last trunk are not connected together by a tie wire 621 as are the others. Consequently there is no ground present on multiple 609 ot the last trunk even it it is busy. In this event, relay 610 releases and prevents further stepping by interposing a break in the circuit of relay 602 in retracting its outer left armature. The sequence switch is advanced from position 5 to position 6 by the release of the slow relay 606, just as in the case of a successful connection.

In position 6, relay 602 energizes over the following circuit: tree pole of battery, relay 602, conductors 620, 628, arm 611 to ground. Relay 602 in attracting its innerI right armature advances the sequence switch to position 7. Ground being present on the multiple 616, relay 602 is held up over the following circuit: free pole of battery, relay 602, inner lett armature and front contact, conductor 632, arm 615, (position 7) to ground on the multiple 616. Contacts 7 to 16 of arm 603 being strapped together and being connected to ground, the sequence switch automatically passes to position 17. Relay 602 1s not deenergir/.ed by the passing of the arm 615 out ot its eighth position because an alternative circuit exists over conductor 633 and arm 601 to the grounded third wire 644. Due to the fact that relay 602 is operated, ground is transmitted from'the inner right armatureV and vliront contact ot said relay, conductors 634 and 635 to side switch arms 611 which extend this ground from positions 9 to 16 to the upper talking conductor. In these positions ground is being transmitted over arm 605 to the lower talking conductor to advance the first selector exactly as in the case oit a busy connection to an ordinary subscriber. l/Vhen the sequence switch reaches position 171 busy tone is transmitted over arms 611 to the upper talking` conductor and thence to the calling subscriber, as in the case of call to a busy ordinary line. rlhe connector stays in position 17 until the calling party hangs up his receiver which results in the release tion 19. ln position 19, relay 602 is oper ated over conductors 620, 626, arms 611 to ground and in attracting its inner right `armature advances the sequence switch to position 20. In passingout of position 19,.arms 611 open the circuit of relay 602 which in retracting its inner right armature advances the sequence switch into position 22 in which position release takes place and sequence switch is restored as described in the case of a successful connection. ln case the desired private branch exchange trunk group terminated in or belonged to a distant office the connection would lead over a first selector of Fig. 1 and one or more selectors such as shown in Fig. 3.

Uormcctz'oas to m operator.

ln case the calling subscriber desires a connection with an operator, he transmits impulses corresponding to a given digit which se s the first. selector in operative relation to a group of trunks each terminating in a jack 707 (Fig. 7) whereupon the selector automatically hunts over the group land picks out an idle trunk. One of these trunks is illustrated in Fig. 7. Assuming therefore that the set of impulses has been transmitted and that the trunk limiting operation has taken place, the relay 106 in releasing its right armature extends grounded third wire 144 to the test multiple 700 o' the selected trunk and` thence to test wire 701, thus causing this trunk to test busy to other selectors. Ground on conductor 701 is connected through the inner left armature and back contact. ot relay 703, lett armature and back contact of relay 704 to the lower talking'conductor of the trunk and 'this ground is also corr nected over lett outer armature talking conductor. This causes the `itirst selector sequence switch to move trom position 5 into position 6. as described in the case of busy call to a local line. Ground upon lead 701 causes relay 702 to operate over a circuit including` the right armatures and back contacts ot relays 703 and 704.

and 4back contact ot the relay 703 to the upper Relay 709ionattracting its right armature' opens-the circuit :of relay702 whichfisaslow 'erated when'4 the release vrelay causingrit to'rein'ove ground fromi lowerftalking. conductor. This Ideen ergizes sequence 'switch ymagnet 104 o'.Z the iirstselector` which in releasing advances thelirst 'selector sequenceswitch vout ot position 6. Itadvances to position 9 in the fob. lowing manner: Relay 133 which was opirst selector sequence switch reached position .6 due to the presence of groundon. the upper talking conductor and thereupon locked up to the third wire 144ias"is-the. caseo'fla'busy call, connects groundl to arrn.118, (position right .arma-r ture.and'backcontact of relay'105, arm `110 (position `7) to the sequence'switch magnet 104causing the switchfto advance to position 8. Ground onthe upper talking` conductor through lead :157 the lower back contact'ofrelay 148, ar1n118, (position 8.)

armature and back contact of relay105, arm

110 to sequence switch magnet104advances the sequence switch to position 9.. Relay 148 in position 8 cannotoperate over arm 1.00 because it is shunted by conductor 157 to the grounded i upper talking' conductor. VVhen the 'operator inserts her answering plug, relay 703 is operated from battery on theA sleeve ofthe plug 706. Relay 703 removesground from the upper talking conductor by 'attracting its leftouter armature 'and`l also opens` t-he circuit. oii'lampy 705.

Ground is connected to lead 701 to hold the 'trunkbusy independent oit the groundv 1 grounded releasel trunk 144 overits righthandarmature and front contact, arm'118, (position 9)`righthand armature and back contact-of relay 105, arm 110, back contact and armature of sequence switch magnet 104 causing the sequence switch to advanceV intov position y10. In passing 'out of position 9 armsll cause'the release of'relay 106. Relay l186 Ais operatednow over the following path: ground on'the upperarmature and -front contact of relay- 103 arm 100, (position 10) relay 186 to battery. The operation of relay 186 extends the talking' conductors from the lineswitch directly to the tirst selector brushes opening the currentfeeding bridges at. the first selector. Relay 186 locks over.` its upper armature and front contact to release conductor 144. The relay 101 isdeenergized upon the operation of relay 186,1causing. relays 102 and 103 to release but duey to the break in the circuit oi' release vmagnet 135y bythe attraction of the lowerfarmature ofrelay 186, the selector is held inits set position. f

The line switch is also held set due to theprevious placingv of. a ground on the third wire 144 from the grounded third wire 7 01, this ground being extended to the wire 144 overf-the rightV retracted. armature rot'.

slay 106.y Thusmthe control of release is with the operator. Talking current is fed to the calling and called Vlines from thebattery in theoperatorscord circuit. When the operator removes plug 706, .relay703 releases removing ground from conductor 701 quenceswitch out of position 10: free pole` of battery, magnet'104, arm 110, (position 10) springs 136, lowerrnost armature of relay 186 and lowermost `armature of relay 108 to gro-und. The sequence switch automatically passes to'normal position. Thus the apparatus `isall `restored ready for the next call. The removal ot ground from the third wire 144 by the removal ofthe lplug causes theline` switch to restore in afwellknown manner.

From `the foregoing it willbe seen that the invention provides an interotlice repeating system which will permit'of the accu.

rate` setting of? automaticI switches irrespective of the length oit trunks, within commercial transmission.limits, and irrespective of the number of trunks and lines over :which the vconnection is built up, and will accurately operate under a wide range fot .variations, obviating delicate adjustmentsot the linger wheel., relays or mechanism ofthe switches.`

ln the systemv of thisinvention, .thegnumber'ot'impulses transmitted by the linger wheel or dial per second may be'materially increasedover systems now in. use without sacrificing accuracy 1n the-'setting of the switches and without increasing cost of' maintenance.-'orstirst costk of the dials.

In systems now. in use,'the.rati0v of the break to them'ake period of tliedial must be maintained within narrow limits,`wlii.ch results in high maintenance as well as first cost. With the arrangement of this invention, a wide range ot variation between the ratio of the make and break periods ot the dialis permissible since the period ot current flow in the stepping magnet is not dependent upon the break period ot the dial.

Consideration ot the circuits show that in order to set the switches at the originating ollice and those switches ot the otlices through which the call progresses, it is only necessary that the impulse relay at each ollice retract its armature tor a period long enough to permit the associated stepping relay 105 to attract its armature whereupon it locks up to the already energized trunk relay 202 and starts the cycle of operations. On the other hand, it is only necessary that the impulse relay at each oitice hold its armature attracted tor a period long enough to permit the associated relay 106 to release its armatureto again connect the stepping relay to the back contact ot the impulse relay. The function oi the relay 106 is to prevent the stepping relay from initiating a second cycle of operations for one and the same retraction ot the armature ot' the impulse relay. The stepping relay `may be arranged to cooperate in .005 oit a second and the relay 106 to release in .00?) ot a 4second. In commercial practice dials transmit about 10 impulses per second which gives about .1 of a second from break to break.

It line conditions are such as to cause the impulse relay 101 to be retracted for very short intervals. the associated relay set nevertheless .goes through its cycle ot operations and positively releases the succeeding impulse -relay once -for each such retraction, which in turn initiates a cycle ot operations ot its relay set to positively release the succeeding impulse relay and so on.

lf, on the other hand7 the line conditions are such as to cause the impulse relay 101 to be retracted for long intervals the associated relay set operates in the samemanner and restores., the relay 106 releasing a fraction of a second after the impulse relay finally pulls up its armature, this relay reconnecting` the stepping relay to the back contact ot the impulse relay7 for the next retraction. By virtue ot the present invention therefore it will be readily appreciated that margins are provided which are more than ample to meet practically any line conditions which may be encountered.

ln actual practice a short impulse transmitted to the stepping magnet ot a selector due to the impulse relay being deenergized ttor a period substantially shorter than the break period caused by the sender. will sometimes cause the selector to be elevated two steps instead of one. rlhe reason tor this is that a locking projection is provided on the selector against which the driving pawl abuts at the end or" its stroke, this projection being so Jformed as to force the pawl into the ratchet and lock it, if the pawl gets a full step. lf the impulse is too short, it ceases betere the pawl reaches the locking projection and the deenergization of the magnet allows the pawl to drop back but the momentum ot the shaft is such as to. carry it up high enough for the holding pawl to engage the second tooth. This will readily be understood ,trom inspection ot Fig. ot Patent 815,176 ot March 13, 1906, see lines 109 to 119 of page 4 thereof.

By virtue ot the present invention this cannot occur since the stepping relay operates on a very short impulse and then locks itself to the back contact ot the step magnet. ln its operated position it closes the stepping circuit and this'impulse does not terminate until the driving pawl reaches the end ot its stroke when it is forced by said, locking projection into the tooth positively locking the shaft. Then the impulse is cutoii by the stepping relay being unlocked due to the driving pawl having reached therequired position.

0n the' other hand if the impulse relay is deenergized for a period substantially longer than the break period caused by the sender this will sometimes cause the selector to be elevated to the level below the one desired. The reason tor this is that the next break period arrives before the impulse relay armature has been attracted long enough` to allow the stepping magnet winding to discharge and consequentlyan impulse'is lost. ln the circuit arrangement ot this invention, this cannot occur inasmuch as the'stepi ping relay is deenergized under the sole control of the stepping magnet armature which in turn in releasing opens the circuit ot the magnet, and the circuit characteristics` are such that this always occurs in time to permit the magnet winding to discharge and be ready for the next impulse when the impulse relay again retracts its armature.

Claims to other features than the repeating system claimed herein will be presented in separate applications.

What is claimed is:

1. ln a machine switching telephone eX- change system, telephone lines, otlices wherein said lines terminate, trunk lines interconnecting said oliices, means at each oilice for producing a cycle ot operations,` an impulse relay at each oi'lice adapted upon the move-` ment of its' armature in one direction to start said means in operation, circuits each including a trunk from one oiiice to the next including the impulse relay thereat, the electrical condition of which is changed by said means while it is going through a cycle of operations, thel` cycle of operations ot each of said means when initiated upon 

